1. Field of the Invention
The present invention relates to a semiconductor integrated circuit interconnect structure and method for fabricating an interconnect structure having enhanced performance and reliability, by minimizing oxygen intrusion into a seed layer and an electroplated copper layer of the interconnect structure.
2. Description of the Related Art
Semiconductor devices include a plurality of circuit components (i.e., transistors, resistors, diodes, capacitors, etc.) connected together to form an integrated circuit fabricated on a semiconductor substrate. A complex network of semiconductor integrated circuit interconnects (interconnects) are routed to connect the circuit components distributed on the surface of the substrate. Efficient routing of these interconnects, across semiconductor devices, requires formation of multi-level or multi-layered patterning schemes, such as single or dual damascene interconnect structures.
An interconnect structure includes metal vias that run perpendicular to the semiconductor substrate. The metal vias are disposed in trench areas. In addition, an interconnect structure includes metal lines that are disposed in the trench areas, wherein the trench areas are formed in dielectric material. The metal vias are connected to the metal lines, and the metal lines run parallel to the semiconductor substrate. Thus, both the metal lines and metal vias are disposed proximately to the dielectric material having a dielectric constant of less than 5.0, which enhances signal speed and minimizes signal crosstalk (i.e., crosstalk refers to a signal being transmitted through a metal line, and affecting another signal being transmitted through a separate metal line, and/or affecting other parts of circuitry in an undesired manner).
Furthermore, an interconnect structure that is copper (Cu) based, when compared with an aluminum (Al) based interconnect structure, provides higher speed signal transmission between large numbers of transistors on a complex semiconductor chip. Accordingly, when manufacturing integrated circuits, copper (i.e., a metal conductor) is typically used for forming the semiconductor integrated circuit's interconnects, because of copper's low resistivity and high current carrying capacity. Resistivity is the measure of how much a material opposes electric current, due to a voltage being placed across the material. However, when copper is utilized to form interconnects, electromigration may occur.
Electromigration is the gradual displacement of atoms of a metal conductor due to high density of current passing through the metal conductor, and electromigration is accelerated when the temperature of the metal conductor increases. Electromigration can result in void formation as well as extrusion/hillock formation along regions of an interconnect structure. The voids can result in an open circuit if one or more voids formed are large enough to sever the interconnect structure, and the extrusions/hillocks can result in a short circuit if one or more extrusions/hillocks are sufficiently long to form a region of abnormally low electrical impedance.
In addition, if an interconnect structure is copper based, oxygen intrusion into copper areas of the interconnect structure causes oxidation of diffusion barrier material of the interconnect structure, wherein an oxidized barrier interface is formed. The oxidized barrier interface is susceptible to serving as an electromigration void nucleation site, which can result in faster growth of large electromigration voids. The oxygen intrusion can be caused by oxygen from moisture in the surrounding dielectric layers and/or by oxygen from other layers (e.g., barrier metal layer) of the interconnect structure. Specifically, oxygen that intrudes the seed layer and electroplated copper layer may consume impurities within the interconnect structure, for example manganese and aluminum impurities, and prevent the impurities from segregating in certain regions of the interconnect structure that are susceptible to copper diffusion.
The segregating of impurities in certain regions of the interconnect structure that are susceptible to copper diffusion is important for suppressing copper diffusion. Copper diffusion can result in an increased amount of void formation and extrusion/hillock formation within the interconnect structure. Thus, if there is insufficient segregation of impurities in certain regions of the interconnect structure that is susceptible to copper diffusion then copper diffusion may not be adequately suppressed. Failure to adequately suppress copper diffusion within the interconnect structure can result in reduced performance and reliability of the interconnect structure due to electromigration.
Furthermore, integrated circuit manufacturers generally have electromigration requirements that should be satisfied as part of an overall quality assurance validation process, but thereafter electromigration may still persist during the lifetime of an integrated circuit in an end-user's computer (i.e., when current flows through the semiconductor integrated circuit's interconnect structure). As a semiconductor integrated circuit interconnect structure is generally formed using copper, which is a metal conductor susceptible to electromigration, electromigration presents a challenge when utilizing integrated circuits with a copper based interconnect structure. The challenge includes void formation and extrusion/hillock formation, caused by electromigration, as well as oxygen intrusion into the seed layer and the electroplated copper layer of the copper based interconnect structure. The void formation and extrusion/hillock formation can reduce integrated circuit performance, decrease reliability of interconnects, cause sudden data loss, and reduce the useful life of semiconductor integrated circuit products.